The present invention relates to gas lasers.
European Patent Publication 0610 170 discloses a gas laser which has a pair of concentric tubular electrodes providing a space therebetween functioning as a discharge chamber in which at least one laser beam runs in the direction in which the beam propagates. Laser gas flows through the chamber, and, the laser gas is supplied in the intake direction and taken out in the gas outlet direction. Although this type of laser construction offers some advantages, there has been recognized a need to increase its efficiency.
It is known that the performance and efficiency of a gas laser are highly dependent on the temperature of the laser gas in the discharge chamber. If a temperature limit, which is in the range of 200xc2x0 C. to 300xc2x0 C. for CO2 lasers, is exceeded, there is a strong detrimental effect on the production of the laser beam. The temperature of the laser gas in the discharge chamber must therefore be kept under the limit mentioned. For this purpose, when the gas laser is operating, the discharge chamber is supplied with laser gas at a relatively low temperature, by means of which the temperature of the laser gas that occurs in the discharge chamber is set or by means of which laser gas heated during the laser process is forced out of the discharge chamber. The degree of cooling of the laser gas that can be achieved in the discharge chamber or the heat taken out of the discharge space is proportional to the volume of laser gas following through the discharge chamber. This in turn depends on the flow speed of the laser gas going through the discharge chamber and on the size of the flow cross section available for the laser gas. Since the length of the discharge chamber in the direction of beam propagation generally far exceeds the width of the discharge chamber, the laser gas to be taken out of the discharge chamber in the beam propagation direction has a relatively long distance to travel and this provides flux losses. As a result, the laser gas is fed to the discharge chamber at a relatively high flow speed, but this may result in high flow losses, which have a negative effect on the efficiency of the whole gas laser.
Accordingly, it is an object of the present invention to provide a novel gas laser in which there is provided improved control of the temperature of the lasing gas and higher efficiency.
It is also an object to provide such a gas laser in which the path of the laser gas through the laser discharge cavity is relatively short.
Another object is to provide such a laser which may be fabricated and operated relatively economically.
It has now been found that the foregoing and related objects may be readily attained in a gas laser having a housing providing an elongated cavity, a first elongated electrode tube within the cavity having an inner diameter and a second elongated electrode tube disposed coaxially within the first electrode tube and having an outer diameter smaller than the inner diameter of the first electrode tube and spaced therefrom so as to provide a gas discharge chamber therebetween. The second electrode tube provides a gas exit chamber therewithin, and the first electrode tube is spaced from the wall of the cavity to provide a gas entry chamber thereabout. Both electrode tubes permit gas to flow therethrough from the gas entry chamber to the gas exit chamber.
Also provided is laser gas circulating means for supplying laser gas to the gas entry chamber and for withdrawing laser gas from the exit chamber, and power supply means for producing a discharge between the electrodes to generate a laser beam travelling axially within the gas discharge chamber. Mirrors at the ends of the gas discharge chamber reflect the laser beam therebetween and provide an exit aperture for the laser beam.
In one embodiment, there is included in the cavity a grid member about the outer electrode tube to effect distribution of the laser gas along the length of the first electrode tube.
The electrode tubes may be fabricated from gas permeable material, and sintered conductive material permeable to the laser gas may be used therefor.
Alternatively, the electrode tubes may be fabricated from a material which is substantially gas impermeable and it has helical slits therein to permit the gas flow therethrough. In one embodiment, the electrode tubes are helical and the coils thereof are axially spaced.
The electrode tubes desirably provide passages for flow of coolant therethrough, and there is included coolant circulating means to provided flow of coolant therethrough.
The laser discharge chamber has at least one wall element extending thereabout and having openings therein for flow of the laser gas therethrough.
As will be appreciated, the flow path of the laser gas going through the discharge chamber of the gas laser is minimized in the interest of the smallest possible flow losses. When the laser discharge chamber is filled, the flow cross section is maximized with laser gas at a relatively low temperature. Because of the gas laser in the design of this invention, the whole generating surface of the electrode tube extending in the beam propagation direction is available for the laser gas exchange.
One important aspect of the invention is the design of the electrode tube through which the laser gas flows in the gas laser in the invention. Electrode tubes of sintered material offer very small resistance to the flow of laser gas, so that a slight pressure difference at the electrode tubes is enough to allow the laser gas to flow through them.